I'll believe they're trustworthy when i see this get closer to an ending. So far, what is presented at the beginning of the game, during the scene with the lawyer and how the behavior of specific characters changed from the aforementioned beginning suggests some of them are up to no good and it will be at the MC's expense. If you want to go forward with believing the opposite, that's your choice.
The only ones i trust right now that have zero impact on the MC getting the full inheritance or even a portion of it are Katie, Lily and Debbie (the sad part is the fact the MC is required by the demands of the will to leave katie if he wants his portion of the money during the scene where you get the second recording). They stand to gain nothing from screwing him over. As far as Jenna, i don't for one second believe the character is as innocent as being depicted. If all the characters really are what cheeky is depicting them as, then ultimately it's going to be a harem ending or multiple endings that lead to having the MC end up with 2 or more of the girls.